Asynchronous programming in .NET

Slides for the C# MeetUp in Barcelona

CPU-bound vs IO-bound, responsive UI in desktop applications, scalability and performance in web applications, obsolete patterns, Task.Run, Task.WhenAll, Task.WhenAny, CancellationToken, Timeout, Progress, performance test with Bombardier, best practices, etc.

Source code samples using .NET Core Preview 4 in https://github.com/gerardo-lijs/Asynchronous-Programming-Samples

Transcript

1. Asynchronous programming in .NET by Gerardo Lijs Twitter @GerardoLijs C# MeetUp Barcelona April 2019
2. Content What is Asynchronous Programming CPU-bound vs IO-bound Obsolete patterns Tasks and async/await Practical use cases • Responsive user interfaces (WPF, WinForms, etc) • Scalability and performance in web applications @GerardoLijs
3. CPU-bound operations • Use Task.Run to execute expensive CPU-bound code in the ThreadPool • Define a Task returning method • In general you will not need other methods of TaskFactory class @GerardoLijs Synchronous method Asynchronous method
4. IO-bound operations • Hard drive • Network • Database • API calls • Hardware read/write (serial port, camera, sensor, etc) @GerardoLijs Unless you work in very specific industries, 95% or more of the code you write will never be CPU-bound. Most of the time you will need asynchronous to deal with IO-bound operations and the times you will use CPU-bound operations you will probably use a library that provides asynchronous methods for you to interact with.
5. Responsive user interfaces @GerardoLijs Demo of a WPF desktop application • Targets .NET Core 3 Preview4 but works exactly the same with .NET 4.7.2 or earlier • The behaviour is the same in WinForms You will need https://dotnet.microsoft.com/download/dotnet-core/3.0 and VS 2019 enabled for .NET Core https://visualstudiomagazine.com/articles/2019/03/08/vs-2019-core-tip.aspx
6. Responsive user interfaces This is bad! Application is not responding @GerardoLijs
7. Responsive user interfaces This is good! Application still responsive with 100% CPU use @GerardoLijs
8. Responsive user interfaces @GerardoLijs
9. Responsive user interfaces • Use async with IO-bound operations whenever possible • Don’t block! • Use async for expensive CPU-bound operations • Use progress report and progress dialogs for better user experience • Allow user to cancel operations when possible • Use benchmarking tools such as BenchmarkDotNet (https://github.com/dotnet/BenchmarkDotNet) Summary @GerardoLijs Source code https://github.com/gerardo-lijs/Asynchronous-Programming-Samples
10. Responsive user interfaces @GerardoLijs Demo of a Web API running IO-bound operation • Targets .NET Core 3 Preview4 but works exactly the same with .NET Core 2 • The behaviour is the same in Web API using .NET 4.7.2 or earlier Source code https://github.com/gerardo-lijs/Asynchronous-Programming-Samples
11. Scalability and performance in web applications Simple API method that downloads a web page using synchronous code @GerardoLijs
12. Scalability and performance in web applications Same method refactored to use asynchronous code @GerardoLijs
13. Scalability and performance in web applications This is bad! This is good! Using async/await @GerardoLijs
14. Scalability and performance in web applications Improves throughput because of reduced number of threads usage, less memory use and less CPU use Asynchronous benefits Source: https://caleblloyd.com/software/net-core-mvc-thread-pool-vs-async/ @GerardoLijs
15. Responsive user interfaces @GerardoLijs Demo of a Web API running CPU-bound operation • Targets .NET Core 3 Preview4 but works exactly the same with .NET Core 2 • The behaviour is the same in Web API using .NET 4.7.2 or earlier Source code https://github.com/gerardo-lijs/Asynchronous-Programming-Samples
16. Scalability and performance in web applications Simple API method running an expensive CPU-bound operation @GerardoLijs
17. Scalability and performance in web applications Same method refactored to use asynchronous code @GerardoLijs
18. Scalability and performance in web applications Synchronous CPU-bound Asynchronous CPU-bound Using async/await makes it worse in this case! @GerardoLijs
19. Scalability and performance in web applications • Use async with IO-bound operations whenever possible • Don’t block! • Don’t use async for expensive CPU-bound operations • Use benchmarking tools such as Bombardier (https://github.com/codesenberg/bombardier) I still need more performance, what can I do? • Scale up • Scale out whole application using Docker/Kubernetes • Scale out only expensive CPU-bound operations to Azure Functions Summary @GerardoLijs
20. Obsolete patterns BackgroundWorker Event-Based Asynchronous Pattern (EAP) Asynchronous Programming Model (APM) @GerardoLijs
21. Task Cancellation • Use CancellationToken in your method and check manually @GerardoLijs
22. Task Cancellation • Use Extension method @GerardoLijs
23. Run a Task with a Timeout • Use Extension method Source: David Fowler -> AspNetCoreDiagnosticScenarios/Scenarios/Infrastructure/TaskExtensions.cs @GerardoLijs
24. Progress reporting • Use IProgress<T> interface • Use indeterminate ProgressRing @GerardoLijs
25. Running asynchronous method synchronously Use helper method borrowed from Microsoft Source: https://cpratt.co/async-tips-tricks/ Call like this Warning Try to avoid this! Most of the times (probably always) there are better ways and you don’t need to run async code synchronously @GerardoLijs
26. Async class constructors They are not available by default in the framework Option 1 - Refactor with InitializeAsync method Call like this Previous class Refactored class @GerardoLijs
27. Async class constructors They are not available by default in the framework Option 2 - Refactor with Factory Pattern Call like this Previous class Refactored class @GerardoLijs
28. Parallel programming @GerardoLijs Demo of a WPF application using TPL and Task.WhenAll • Uses ReactiveUI and MahApps but they are not a requirement • Uses OpenCvSharp library as example of expensive operations • Targets .NET Core 3 Preview4 but works exactly the same with .NET Core 2 • The behaviour is the same in Web API using .NET 4.7.2 or earlier https://github.com/gerardo-lijs/Asynchronous-Programming-Samples Source code
29. Slides, resources and source code Gerardo Lijs Software Developer At Microptic SL Email gerardo.lijs@gmail.com Twitter @GerardoLijs https://github.com/gerardo-lijs/CSharpMeetup-Mar2019 Thank You! https://github.com/gerardo-lijs/Asynchronous-Programming https://github.com/gerardo-lijs/Asynchronous-Programming-Samples